Cell-based immunotherapy is a therapy with curative potential for the treatment of cancer. T cells and other immune cells may be modified to target tumor antigens through the introduction of genetic material coding for artificial or synthetic receptors for antigen, termed Chimeric Antigen Receptors (CARs), specific to selected antigens. Targeted T cell therapy using CARs has shown recent clinical success in treating hematologic malignancies.
Multiple myeloma (MM) is the second most common hematologic malignancy.9 Approximately 25% of patients have high-risk cytogenetics, which portends a median survival of less then 2 years.10,11 While recent strides have been made, regardless of cytogenetics, the disease is still considered incurable outside the immuno-therapeutic graft versus myeloma (GvM) effect of an allogeneic transplant. However, allogeneic transplants are limited by ineligibility and high rates of transplant-associated morbidity and mortality.12 Similar to the GvM effect, a potentially curative T cell effect may be achieved with minimal toxicity through autologous adoptive T cell therapy.
Myeloma may be an ideal disease to test adoptive T cell therapy. First, as indicated above, allogeneic transplants demonstrate that the T cell can be a curative treatment, even with minimal or no concomitant chemotherapy such as after non-myeloablative transplants or post-transplantation donor lymphocyte infusions. Second, conditioning chemotherapy, possibly through the mechanism of depleting regulatory T cells (Tregs), enhances the efficacy of adoptive T cell therapy,5,13 as such, the immediate post-autologous transplant period could be an optimal time to administer T cells, and myeloma is one of the few diseases where autologous stem cell transplantation is the standard of care. Third, the immunomodulatory drug lenalidomide may improve CAR based therapy, as has been shown in mice,14 and lenalidomide is commonly used to treat MM. Fourth, adoptive T cell therapy works best in bone marrow predominant disease such as ALL,7,8 when compared to solid tumors or extra-medullary CLL,5 and similar to ALL, myeloma is a disease of the bone marrow.
While there are various reasons to expect that adoptive T cell therapy may work well in MM, expanding adoptive T cell therapy to myeloma also poses unique challenges. Unlike other B-cell malignancies, CD19 expression is seen in only 2% of myeloma patients.15 Furthermore, unlike CD19, the common extracellular immunophenotypic markers in myeloma (CD138, CD38, and CD56) are all co-expressed on other essential cell types, and we predict CARs to any of these targets would lead to unacceptable “off tumor, on target” toxicity7 which can be fatal even in targets where antibodies are well tolerated, as was the case with a HER2 targeted CAR.16 To address these challenges, we have identified extracellular targets with predicted high MM and limited essential normal tissue expression that may be optimal targets for adoptive T cell therapy of MM. Accordingly, there are needs for novel therapeutic strategies to design CARs targeting antigens that are highly expressed in MM cells and limited expression in normal tissues for treating multiple myeloma, which strategies capable of inducing potent tumor eradication with minimal toxicity and immunogenicity.